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Wind turbine test site seeks breaking point

With tomorrow’s wind turbines being built to nearly the length of a football field, technicians in a huge steel box in Charlestown are conducting tests to ensure their safety and reliability in creating green energy

At nearly 200 feet long, it is among the largest windmill blades in the world, so big it had to be brought in on a cargo ship to a testing center in Charlestown, where two hydraulic cranes were necessary to move the 13-ton fiberglass and balsa wood structure.

Over the next year, the Wind Technology Testing Center will bend, oscillate, and ultimately break the massive, hollow blade, testing its strength and looking for flaws in its construction and design that could influence the future of wind power.

With wind power becoming more mainstream, the industry is going big — designing taller turbines with longer blades that can generate more electricity. That means fewer of the massive machines may be needed for each wind farm, which could result in less disruption to the landscape wherever they are built.

Opened in 2011 with the help of state and federal money, the Wind Technology Testing Center is one of the largest such facilities in the world. A cavernous steel box similar to an airplane hangar, the center has two overhead cranes that can each hoist 50 tons, and reinforced concrete blocks that hold blades on a horizontal axis while workers subject them to multiple stress and fatigue tests.

The bending test, for example, is administered with winches and cables, and is expected to make the huge blade bow nearly 42 feet without snapping it — though eventually it will do just that.

To handle the kind of force needed to make blades move so much, the testing center was designed with a special frame and joints that allow the building to sway and adjust, much like a diaphragm, to absorb stress. The building itself is anchored into bedrock with cement casings that are up to 185 feet below ground.

Built at a cost of nearly $40 million, the Charlestown center has so far put 16 other turbine blades to the test, though none as large as the 200-foot-long blade. In part because it will be tested to failure, the blade’s maker has not been disclosed.

Just outside the building are remnants of several other blades, now just pieces of fiberglass and balsa in a pile.

“Our clients are very particular about how they break,” Yarala said, and his staff often must sign nondisclosure agreements.

The center is large enough to test a blade as long as 300 feet — though none that big have been built yet.

In the United States right now, blades on a typical wind turbine — which averages 1.87 megawatts of generating capacity — stretch about 150 feet from end to end. The 3.6-megawatt turbines scheduled to be installed at the Cape Wind farm off the coast of Massachusetts will be 165 feet long.

Meanwhile, Vestas Wind Systems, a Danish turbine maker, is currently testing a prototype blade that stretches some 260 feet, and Yarala said he believes that’s about the size of the longest blades in use now. Sandia National Laboratories, meanwhile, plans to build a 328-foot blade.

Why is bigger better? The larger the area that turbine blades can sweep, the more power they extract from the wind, said Emily Williams, a senior policy analyst at the American Wind Energy Association, a trade group.

But the longer blades are too big to move by truck. The 200-foot specimen in Charlestown arrived on the cargo ship Thorco Adventure. Workers in neon-yellow safety vests and hard hats used twin hydraulic cranes to lift it from the ship’s deck and guide it onto an extra-long truckbed for the short trip to the center.

Yarala said it can take six months to run a blade through a standard battery of tests, which includes making it undulate to simulate the conditions that cause wear and aging, and pulling the blade to see how far it bends. “There’s a balance between how much you want them to flex and when they break,” he said.

Inside the center on a recent morning, a worker used a bucket lift to help him remove cables from the large blade, which had just undergone a test in which it was made to vibrate.

The data collected from dozens of sensors attached to the blade will help workers analyze the design of the wing-like structure.

Outside, just beyond the pile of broken blades, four smaller blades were soon to be rolled into the facility, where they would be outfitted with sensors and maneuvered into a wall-mount for testing.

Another blade is expected to arrive before the end of the year. “That keeps us busy for months,” Yarala said.

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